1. Field of the Invention
The present invention relates to a heating apparatus, as well as to a processing apparatus employed in the manufacture of a semiconductor device.
2. Discussion of the Background
The manufacturing process of a semiconductor device comprises in general the step of forming a thin film on an object to be processed, e.g., a semiconductor wafer, by using a CVD apparatus or a sputtering apparatus in order to form an integrated circuit on the semiconductor wafer. It should be noted that a nonuniform thickness of the thin film, which is caused in the film-forming step, leads to a low yield of the product integrated circuit element. The nonuniform thickness of the film is derived from a nonuniform temperature distribution over the semiconductor wafer surface in the step of heating the wafer, i.e., the object to be processed. Naturally, it is very important to keep the temperature uniform over the entire surface region of the wafer in the film-forming step.
In the conventional heat treating apparatus of a lamp heating type, in which the object to be processed is heated with energy rays, an object to be processed, e.g., semiconductor wafer W, is disposed on or within a process chamber. A processing gas is supplied by a gas supply means through a processing gas supply and a porous plate onto the surface of the wafer W within the process chamber. Also, the inner space of the process chamber communicates with an exhaust means via an exhaust port so as to keep the inner space of the process chamber at a predetermined degree of vacuum.
A heating chamber having a heating means disposed therein is arranged below the process chamber. The heating means, which consists of a heating lamp and a reflecting mirror, is arranged on a rotatable table.
A transmitting window is formed in a bottom portion of the process chamber. The light generated from the heating means is transmitted through the transmitting window so as to irradiate the wafer W with the light.
The heating means is divided into a plurality of different sets of the heating means. In accordance with rotation of the rotatable table supporting the heating means, these different sets of the heating means are allowed to form different annular heating regions 11, 12, 13 in the wafer W, as shown in FIG. 1. The heat energy supplied to these annular heating regions 11, 12, 13 can be controlled independently.
A cooling air is introduced through a cooling air supply port into the heating chamber by a cooling air supply means so as to cool appropriately the heating chamber, transmitting window and heating means.
In the lamp heating type heat treating apparatus of the construction described above, it is certainly possible to improve the uniformity of the temperature distribution in a radial direction over the entire surface of the wafer W by independently controlling the heat energy supplied to the annular heating regions of the wafer W. However, the conditions for the heat absorption and heat emission achieved by the wafer W are affected by the contact between the table and the semiconductor wafer W, the cooling air introduced into the heating chamber, and by asymmetry in the shape and material of the process chamber, resulting in failure for these conditions to be rendered uniform over the surface of the wafer W. It follows that the temperature distribution tends to be rendered nonuniform in the circumferential direction of the wafer W, making it difficult to keep the temperature of the wafer W uniform over the entire surface of the wafer W during the heat treatment.
It should also be noted that the conventional lamp heating type heating apparatus is constructed such that a cooling air is blown against all the heating lamps arranged within the heating chamber. In this construction, it is difficult to cool uniformly all the heating lamps.
In general, a halogen lamp is used as the heating lamp. In the halogen lamp, a halogen cycle is repeated, in which a filament component such as tungsten is evaporated to form a halogen compound and then, the halogen compound is decomposed such that the evaporated filament component is brought back to the filament. What should be noted, however, is that, if the temperature distribution is rendered nonuniform over the surface of the lamp body, i.e., bulb, the halogen compound is deposited on the low temperature region on the bulb surface, making it difficult to permit the halogen cycle to continue smoothly. As a result, the filament tends to be broken easily, leading to having low durability the heating lamp and, thus, to a short life of the lamp.
It should also be noted that the heating lamp is sealed in general by allowing a quartz glass of the lamp body to be bonded to an electrically conductive member such as a molybdenum foil. Therefore, if the sealing portion is heated excessively, a clearance is generated between the conductive member and the quartz glass because of the difference in the thermal expansion coefficient between the two. Naturally, the halogen gas is likely to leak to the outside through the clearance, leading to a low durability of the heating lamp.
In order to obtain a semiconductor device exhibiting satisfactory electrical characteristics, it is important to form a satisfactory film. Particularly, it is important to form a film of a uniform thickness on the wafer surface. It should be noted in this connection that the film-forming rate is markedly affected by only a small temperature difference. In other words, the wafer temperature must be kept uniform over the entire wafer region in order to form a film of a uniform thickness on the substrate surface.
The apparatus exemplified above is a so-called cold wall type processing apparatus in which the side wall of the process chamber is kept at substantially room temperature. Therefore, heat is released at, particularly, the peripheral portion of the table in a considerably large amount. In addition, the processing vessel is required to be miniaturized as much as possible. Naturally, the space for housing the heating lamps is very limited, making it necessary to increase the density of the lamp arrangement as much as possible. Under the circumstances, vigorous studies are being made as to how to arrange the heating lamps and how to perform the heating treatment in an attempt to ensure high uniformity of the temperature over the entire surface of the wafer. However, a satisfactory measure for achieving the object has not yet been reached. It should be noted in particular that the wafer size of 6 inches, which was popular in the past, is now being changed to 8 inches and, further, to 12 inches. If the design idea adapted for the semiconductor device involving a wafer size of 6 inches is applied as it is to the device involving a wafer size of 6 inches or 12 inches, a subtle temperature imbalance is brought about, leading to unsatisfactory results.